Occlusal caries (decay) account for nearly half of all caries occurring in the human population. Certain adhesive materials have been shown to be effective in sealing the pits and fissures of the occlusal tooth surface, to thereby prevent or reduce the incidence of various attacks. One of the deficiencies of existing pit and fissure sealants is that colorless nature makes it difficult for the dentist to evaluate the integrity of the protective sealant during periodic examination, and also during application of the sealant to make sure that all the desired surfaces have been coated or, alternatively, to make sure that an excessive amount of coating has not been applied to certain areas. Inorganic pigments have been used to render the sealant more visible, such as the titanium dioxide pigment disclosed in U.S. Pat. No. 4,150,012. However, such inorganic pigments alter the viscosity of the sealant which can affect the sealant's properties. Further, the pigments tend to render the sealant opaque which makes it impossible for the dentist to visually assess the status of the tooth enamel under the sealant.
There has not been available a suitable sealant composition which can be readily detected on the tooth's surface, yet which is still transparent enough to permit the dentist to visually examine the surface of the tooth through the sealant. For esthetic reasons, only lighter color dyes are acceptable. Dark colors such as black, blue, and green are not esthetically pleasing and are, therefore, unacceptable.
Since sealants are used in the mouth, only dyes which are judged safe for internal use should be considered In the United States, the Food and Drug Administration (FDA) has listed compounds which can be certified for use in foods, drugs, and cosmetics (FD&C), and those which can be certified for use in drugs and cosmetics, D&C. Unfortunately, all but one of the FD&C certified dyes have been found to be insufficiently soluble in acrylic sealants to be usable therein, and the one having sufficient solubility (Red No. 3), is also water-soluble and tends to leach out in the presence of water. Also, all of the D&C colorants which are soluble in organic compounds are currently restricted to very specific uses, none of which include the use of coloring dental restorative materials. Thus, none of the certified dyes which one skilled in the art would select can be used for tinting a pit and fissure sealant if one adheres to FDA guidelines.
Another class of coloring agents which can be used in foods in the United States includes vegetable and plant extracts. These materials and their extraction method are described in the U.S. Code of Federal Regulations 21, part 73. These compounds being natural products, are usually water soluble and are therefore unacceptable for use in an organic monomer such as an acrylic sealant. A few of these plant extracts are soluble in animal fats and vegetable oils and are used to color such products as butter, cheese, margarine, and vegetable oils. Typical examples of such products are Annatto, Turmeric, and .beta.-Apo-8'-Carotenal. However, from the structure of the principal colorant contained in each of the above, one would not expect these materials to be acceptable for use in a free radical polymerized acrylic system. All of these compounds derive their color from a highly conjugated vinyl system. Thus, one would expect these bonds to be attacked during the free radical polymerization of the chemically similar vinyl monomers, which would result in a disruption of the chromophore with subsequent loss of color. Further, one would also expect that the Curcumin, which is found in Turmeric extract, to act as an anti-oxidant to retard polymerization because it contains phenolic groups.